1. Technical Field
The present invention relates to a system and method for automatically topping up an internal combustion engine with lubricant.
2. Background Art
Various systems for automatically topping up the sump of an internal combustion engine with oil are well known.
Such a system is described in EP 0638708 B1. When the engine is started, in the system described, oil is drawn into the sump from an external oil container by means of negative pressure. When a maximum permitted oil level is reached, an oil level sensor sends a signal to an electrically controlled valve, and topping up with oil is thus stopped. The oil then circulates for a certain time through the external oil container back to the sump. In this way, the oil in the external container is mixed with oil from the sump. Although it is relatively simple, this system has several disadvantages. One disadvantage is that oil is topped up only when the engine starts. When it is cold and the oil is of high viscosity, the oil will flow out slowly, which results in the oil level in the sump not being the same everywhere during topping up. This in turn leads to the quantity of oil in the sump being too great when the level sensor reacts. Another disadvantage of this system is that it utilizes a sensor that stops the topping-up process. In the event of functional problems in the sensor circuit, the entire external oil quantity can end up in the sump. A third disadvantage is that the system requires an oil level sensor mounted in the sump, where it is exposed to vibrations, temperature cycles, old oil, and other detrimental conditions. A further disadvantage is that the oil in the external container is mixed with oil from the sump. When the oil is changed, the oil in both the sump and the external container must be changed and the external container also has to be cleaned.
Another such system is described in EP 0416688 A1. The system described in that specification consists of an external oil container, an electrically controllable valve, a measuring container, a level sensor, an internal combustion engine with an oil sump and a programmable control unit. The oil container is connected to the electrically controllable valve which is in turn connected to the measuring container. The measuring container is connected to the sump according to the principle of communicating vessels so that the oil level of the sump can be measured in the measuring container by means of the level sensor.
The control unit measures the oil level in the measuring container by means of the level sensor before the engine is started; that is to say, in the first position of the ignition switch. If the level sensor provides a signal that the oil level is correct, the engine can be started. If the oil level is too low, a topping-up operation is initiated in which a predetermined quantity of oil is filled into the measuring container and thus into the sump via the electrically controllable valve. The oil level is then measured again. If the oil level is correct, the engine can be started; otherwise another topping-up operation is carried out. If the oil level is still too low, an error signal is generated and the ignition switch is locked. The oil level then has to be inspected manually. The engine can be started using an emergency unit.
This system also has several disadvantages. Above all, it is complicated and contains many components; for example, electrical components, that can give rise to reliability problems, which can lead to operation being disrupted. As the oil level is measured in the measuring container, which is located outside the sump, even a slight inclination of the vehicle can result in the sump containing more oil than necessary, which can lead to increased friction losses (splash losses), more oil mist in the blow-by gases and thus higher oil consumption. The measuring container is connected to the sump via a pipe which is located in a highly exposed position at the bottom of the engine. If this pipe is damaged, the engine is emptied of oil. Moreover, this solution is costly.